This invention relates to an adhesive composition comprising a blend of one or more silane functional prepolymers and one or more isocyanate functional prepolymers and to a method of bonding two or more substrates together using the adhesive composition. Preferably, a window is bonded to a window flange using the adhesive of the invention.
Polyurethane sealant compositions are used for bonding non-porous substrates, such as glass, to nonporous substrates; these are described in Berger et. al., U.S. Pat. No. 4,374,237 and Rizk et. al., U.S. Pat. No. 4,687,533, both incorporated herein by reference. Berger et. al., U.S. Pat. No. 4,374,237 describes a polyurethane sealant containing urethane prepolymers which have been further reacted with secondary amine compounds containing two silane groups. Rizk et. al., U.S. Pat. No. 4,687,533 describes a polyurethane sealant containing urethane prepolymers which contain silane groups which have been prepared by reacting a polyisocyanate having at least three isocyanate groups with less than an equivalent amount of an alkoxysilane having a terminal group containing active hydrogen atoms reactive with isocyanate groups to form an isocyanatosilane having at least two unreacted isocyanate groups. In a second step, the isocyanatosilane is mixed with additional polyisocyanate and the mixture is reacted with a polyol to form a polyurethane prepolymer having terminal isocyanato groups and pendant alkoxysilane groups.
Hattori et. al., EP 856,569 discloses the use of polyoxyalkylene polymer terminated with silanes having hydrolyzable groups bonded thereto blended with a polyoxyalkylene polymer having no cross-linking groups to bond glass to metal. Wu, U.S. Pat. No. 6,649,016 discloses an adhesive which bonds primerless to painted substrates comprising: A) one or more polymers having a flexible backbone and silane moieties capable of silanol condensation; B) one or more titanates or zirconates having one or more ligands comprising hydrocarbyl phosphate esters and/or a hydrocarbyl sulfonate esters; and C) an anhydrous strong organic acid which is miscible with the polymer and enhances the bonding of the adhesive to a coated substrate in the absence of a primer. Hsieh et al., U.S. Pat. No. 6,015,475 discloses an isocyanate functional prepolymer based adhesive composition which bonds primeness to painted substrates.
Such sealants are used to bond glass substrates to painted substrates. Typically, a separate glass primer comprising a solution of one or more silanes is typically applied to the glass substrate prior to the application of the adhesive. This is the case in most vehicle assembly operations for bonding the windshield and the rear window to the vehicle. The use of a primer in assembly operations is undesirable in that it introduces an extra step, additional cost and exposes the assembly line operators to additional chemicals.
The automobile producers demand an adhesive for bonding glass into a vehicle which cures rapidly so that the vehicle can be moved without the glass falling out or slipping from the desired location. Additionally, it is important that the adhesive demonstrate stability prior to application, that is does not cure before being applied to bond the glass into the vehicle. If the adhesive cures in the delivery system in the auto plant, the assembly line must be shut down while the adhesive delivery system is purged. Such a shut down is very costly for the automotive companies and must be avoided. Automobiles last upwards of 10 years and the adhesive needs to maintain its' integrity and hold the window into the vehicle for the life of the vehicle under a variety of difficult conditions. Thus, what is needed is an adhesive which can bond to the automotive paints, especially difficult to bond to paints, and glass; which can bond windows into a vehicle without the need to use a primer, which adhesive also demonstrates strong adhesion, rapid adhesive strength build up, fast link-up, good stability and long term durability.